The overall objective of our research program is to determine the structure, mechanism of action, physiological function, and cellular disposition of certain kidney peptidases. Specifically, the enzymes under study are the zinc metallo-enzyme, renal dipeptidase, and the antidiuretic hormone-inactivating peptidase isolated from renal plasma membranes. The role of renal dipeptidase in dipeptide hydrolyses and transport within the brush border microvilli of the kidney will be investigated. Using the facile spectrophotometric assay for renal dipeptidase, urinary renal dipeptidase levels in urine obtained from patients with kidney tubular disorders will be determined. Urinary renal dipeptidase will be isolated, purified and characterized using techniques previously developed for the membrane-bound enzyme. Studies on the mechanism of action of renal dipeptidase will include spectroscopic analysis of the cobaltous derivative of the zinc metalloenzyme. Finally, isolation and characterization procedures will be employed to study the antidiuretic hormone-inactivating peptidase recently located in plasma membranes of the kidney medulla.